1. Field of the Invention
The present invention relates to a rolling bearing apparatus with a supply unit that supplies a slight amount of lubricant to a bearing portion and a lubrication unit that supplies a slight amount of lubricant to rotating components such as a rolling bearing.
2. Description of Related Art
Rolling bearings are used as spindle bearings for machine tools. Some rolling bearings adopt oil-air lubrication in order to ensure appropriate lubrication of the rolling bearing (see, for example, Japanese Patent Application Publication No. 2009-58091 (JP 2009-58091 A)). However, the oil-air lubrication involves high running costs due to air consumption and needs incidental facilities such as an oil-air supply apparatus and an air clean unit, possibly leading to high facility costs.
As another means for lubricating a rolling bearing, a bearing apparatus incorporating a lubrication unit is known (see, for example, Japanese Patent Application Publication No. 2004-108388 (JP 2004-108388 A)). In the bearing apparatus, an annular lubrication unit is installed on a fixed bearing ring (fixed ring) of an inner ring and an outer ring, and the rolling bearing and the lubrication unit are integrated together. The lubrication unit includes a tank in which a lubricant is stored and a pump that discharges the lubricant in the tank into an annular space between the inner ring and the outer ring.
A slight amount of lubricant is discharged from the pump. The amount of lubricant discharged is adjusted by controlling operations of the pump. In a bearing apparatus including such a lubrication unit as described above along with a rolling bearing, a slight amount of lubricant can be discharged into the annular space formed between the inner ring and the outer ring. The discharged lubricant adheres to raceway surfaces of the inner and outer rings and to rolling elements, thus allowing the rolling bearing to be lubricated.
For a tank for the lubrication unit as described above, it is conventionally preferable that an outlet port (outlet portion) through which the lubricant flows out be formed at the lowest position. The reason is as follows. If the outlet port is formed at a slightly high position in the tank, when the amount of the lubricant decreases to the degree that the surface of the lubricant is lower than the outlet port, air in the tank flows out through the outlet port. Furthermore, the lubricant in an area lower than the outlet port remains unused. Thus, in the related art, when the outlet port is not formed at the lowest position, the lubricant in the tank may fail to be used up.